Light Source

ABSTRACT

The invention relates to a light source comprising a primary radiation source and a luminescent substance, and to a method for producing this light source. The invention relates, in particular, to a method for producing an electric light source using one or more luminescent substances emitting in the visible spectrum range, and at least one primary source emitting preferably in the UV range, and which is preferably, but not exclusively, an LED.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims the priority benefit of PCT/EP2007/009471 filedon Oct. 31, 2007 and German Application No. 10 2006 051 756.3 filed onNov. 2, 2006. The entire contents of these applications are herebyincorporated in their entirety.

BACKGROUND

The invention relates to a light source comprising a primary radiationsource and a luminophore, and to a process for producing such a lightsource. The invention relates especially to a process for producing anelectrical light source using one or more luminophores which emit in thevisible spectral region and at least one primary source which emitspreferably in the UV and is preferably but not exclusively an LED.

SUMMARY OF THE INVENTION

Light sources based on at least one LED are realized through combinationof a primary source which emits in the UV and one or more luminophoreswhich are excited by the UV light of the primary source and emit in thevisible spectral region. In an illustrative embodiment, a Ga(In)N LEDwhich emits at about 460 nm and a yellow-emitting YAG: Ce³⁺ luminophore(WO 98/12757) are used. When the aim is a pure white light source, aplurality of different luminophores have to be used, generally onematerial each emitting in the red, green and blue. According to theprior art, these have to be adjusted to an optimal particle size in eachcase and generally provided with a transparent protective layer.Finally, they are applied, as a mixture or embedded individually into apolymer matrix, to the primary source, for example a Ga(In)N LED (WO2006/061778 A1 and U.S. 2003/0052595 A1). This process comprises severalindependent steps and is obviously very complex. Furthermore, in theinterests of a high lifetime of the illuminants, high demands are madeon the UV and thermal stability and the optical transparency of theprotective layers and polymer matrix. In particular, in view of the factthat the new LED-based light sources will be mass-market products, theproduction process should have a high potential for automated and henceinexpensive production.

It was thus an object of the present invention to overcome the outlineddisadvantages of the prior art and more particularly to provide a lightsource which can be produced in a simple manner, and which enables theemission of white light.

This object is achieved in accordance with the invention by a lightsource comprising (i) a primary radiation source and (ii) a luminophorelayer or a luminophore based on an amorphous or partly crystallinenetwork, said network comprising nitrogen (N) and at least two elementsselected from P, Si, B and Al, and at least one activator beingincorporated into the network.

The inventive light source comprises, as constituent (i), a primaryradiation source. This primary radiation source can in principle emitlight in any desired wavelength range. It preferably provides UVradiation, especially within a wavelength range from 250 to 450 nm, morepreferably from 300 to 430 nm. More preferably a peak maximum of theemission of the primary radiation source is within the ranges specified.The primary radiation source is more preferably an LED (light-emittingdiode), especially a GaN or Ga(In)N LED. The light emitted by theprimary radiation source is also referred to herein as primaryradiation.

The inventive light source further comprises a luminophore layer and aluminophore, respectively, based on an amorphous or partly crystallinenetwork, said network comprising N and at least two elements selectedfrom P, Si, B and Al, and at least one activator being incorporated intothe network.

The luminophores used in accordance with the invention are notableespecially in that they are not substances based on a crystallinenetwork, but rather substances based on an amorphous or partlycrystalline network. The base materials used to form the luminophorehave networks which are especially X-ray-amorphous, i.e. they have nocrystals with a diameter of ≧300 nm, especially no crystals with adiameter of ≧200 nm and even more preferably no crystals with a diameterof ≧100 nm. The base material of the luminophores thus especially has nolong-range lattice symmetry whatsoever. Additionally incorporated intothe network of the base material in the luminophores is at least oneactivator. In contrast to conventional crystalline luminophores, thereis no exchange of ions present beforehand in the base material foractivators, and the activators are instead incorporated additionally.This brings the significant advantage that any desired activators can beincorporated into the same matrix, and it is thus possible to provideluminophores which comprise different activators.

DETAILED DESCRIPTION

The base material of the inventive luminophores, which comprises anamorphous or partly crystalline network, comprises at least two elementsselected from P, Si, B, Al and also, independently thereof, always N. Inparticular, the network consists of the elements P, Si, B, Al and N, orthe particular subsystems of P, Si, B and N, P, Si, Al and N, Si, B, Aland N, P, B, Al and N, P, Si and N, P, B and N, P, Al and N, Si, B andN, Si, Al and N or B, Al and N. Suitable activators are incorporatedinto this network. The activators incorporated into the inorganicamorphous or partly crystalline network may especially be any desiredmetal ions. Preferred activator elements are Ba, Zn, Mn, Eu, Ce, Pr, Nd,Sm, Tb, Dy, Ho, Er, Tm, Yb, Sn, Sb, Pb or Bi. The activators arepreferably Mn²⁺, Zn²⁺, Ba²⁺, Ce³⁺, Nd³⁺, EU²⁺, Eu³⁺, Gd³⁺, Tb³⁺, Sn²⁺,Sb³⁺, Pb²⁺or Bi³⁺. The amount of activators in the luminophore ispreferably ≧0.1% by weight, especially ≧0.5% by weight, and preferablyup to 14% by weight, especially up to 5% by weight. The activators mayalso have a sensitizer function.

The luminophore emits preferably at wavelengths between 480 and 740 nm.The luminophore preferably absorbs the primary radiation verysubstantially completely. It is additionally preferred that the lightemitted by the luminophore has different wavelengths than the lightabsorbed. Since, in accordance with the invention, there is no exchangebut instead an introduction of the activator elements, it is alsopossible for any desired combinations of activator elements to beintroduced into the luminophore and thus, more particularly, for theemission colors to be adjusted as desired. More preferably, theactivators are combined such that white light is emitted.

More preferably in accordance with the invention, suitable activatorsare incorporated into an amorphous three-dimensional network of thecomposition Si/B/N. This host material has no periodic lattice symmetrywhatsoever.

Owing to advantageous effects on the crystal field strengths for theactivators, and in order to achieve a high thermal and mechanicalstability, the base material structure is preferably of nitridic nature,which may optionally be doped oxidically.

According to the invention, the luminophore or the luminophore layer mayfurther comprise fillers. Preference is given to solid particles asfillers, which at the same time have a light-scattering action. Suchsolid particles are, for example, SiO₂, TiO₂, SnO₂, ZrO₂, HfO₂ and/orTa₂O₅. The solid particles preferably have a narrow particle sizedistribution, the mean of the particle size distribution, depending onthe refractive index of the particular material, preferably beingselected such that white light is scattered optimally.

The layer thickness of the luminophore or of the luminophore layer ispreferably between 200 and 3000 nm, especially between 300 and 2000 nm.

According to the invention, the luminophore layer may be in directcontact with the primary radiation source, i.e. be applied directly tothe primary radiation source. However, it is also possible to arrangethe luminophore layer in indirect contact with the primary radiationsource, which means that further materials or layers are arrangedbetween the primary radiation source and the luminophore layer. Theintermediate layers or intermediate materials for the primary radiationare preferably completely transparent.

The invention further relates to a process for producing a light sourceas described herein, which is characterized in that a luminophoreprecursor is applied directly or indirectly in liquid form or as asuspension to a primary radiation source and then hardened.

The invention provides, more particularly, a process for liquid-phasecoating of a primary source with a luminophore which emits in thevisible spectral region. The process according to the invention is basedon a new family of luminophores consisting of an amorphous matrix, intowhich all conceivable activators can be introduced in widely variableconcentrations. This very advantageous feature is brought about byvirtue of the fact that the activators are incorporated notsubstitutively, i.e. replacing a matrix atom, but instead additively.

This novel class of luminophores is obtained proceeding from molecularprecursors via an oligomeric or polymeric intermediate and the finalstep of a pyrolysis. When the molecular precursors with the activatorsdissolved therein or the partly crosslinked preceramic oligomers areliquid, they can be applied, for example, by dip-coating, spin-coatingor spray-coating, then fully crosslinked by heating in an ammoniaatmosphere and converted to a firmly adhering ceramic layer bypyrolysis.

In a first preferred embodiment, a mixture of at least one molecularprecursor, at least one activator and optionally fillers is formed andapplied to the primary source. This is followed by hardening, especiallyby ammonolysis and subsequent pyrolysis. The viscosity of the mixture tobe applied to the primary source can be adjusted here by the type andthe content of the fillers.

In a further preferred embodiment, a mixture of at least one molecularprecursor, at least one activator and optionally fillers is likewiseapplied to the primary source, although this mixture has first beensubjected to a partial hardening, for example a partial ammonolysis, inorder to adjust the viscosity to the desired value. This is followed bythe application to the primary source and, thereafter, the hardening tocompletion, for example by ammonolysis and pyrolysis.

In a further preferred embodiment, the molecular precursors, theactivators and optionally fillers are first used to form a preceramicpolymer. This preceramic polymer is obtained, for example, by a completeammonolysis. This preceramic polymer is then applied to the primarysource. Liquid preceramic polymers can be applied directly. If thepreceramic polymer is resinous or solid, a fine suspension of thepreceramic polymer in a solvent is advantageously formed, and thissuspension is applied to the primary source. The solvent is thenevaporated and the luminophore layer is subsequently hardened, forexample by pyrolysis.

It is additionally possible in accordance with the invention to addconventional solid pulverulent luminophores to the starting materialsfor the luminophore layer. Such an addition can result in fineadjustment of the emission.

The base material of the luminophores used in accordance with theinvention is obtainable especially via molecular precursors which areprocessed to a preceramic material which is then converted to the finalceramic state by pyrolysis. The luminophore can be applied to theradiation source in the form of a molecular precursor or be formed froma molecular precursor.

To this end, one or more molecular precursors are first provided. Themolecular precursors contain the elements of the base material, i.e.more particularly, at least two elements, preferably at least threeelements, selected from P, Si, B and Al. The concentrations of P, Si, B,Al are preferably adjusted in each case between 0 and 100 atom %, morepreferably between 10 and 80 atom %. The molecular precursors are morepreferably halides, preferably chlorides.

It is possible to use several molecular precursors as the startingmaterial, especially a mixture of molecular precursors which are thensubjected to a co-ammonolysis. Mixtures of molecular precursors can beobtained, for example, by mixing a silazane and a boron halide and/orphosphorus halide.

In a further embodiment, a molecular precursor is used, which is aone-component precursor. Such a one-component precursor already containsall elements of the product. Particular preference is given to using, asthe starting point of the preparation, the molecular compoundCl₃Si(NH)BCl₂ (TADB), which already contains the Si—N—B linkage desiredin the end product.

Further preferred molecular one-component precursors areCl₄P(N)(BCl₂)SiCl₃, Cl₃PNSiCl₃, (Cl₃Si)₂NBCl₂, Cl₃SiN(BCl₂)₂,(H₃Si)₂NBCl₂, Cl₃Si(NH)(BCl)(NH)SiCl₃, Cl₃Si(NH)(AlCl)(NH)SiCl₃,[(Cl₃Si)(NH)(BNH)]₃, (Cl₃Si(NH)AlCl₂)₂ or [Cl₃PN(PCl₂)₂N]⁺[AlCl₄]⁻.

The precursor material is then hardened to give a luminophore whichcomprises an amorphous or partly crystalline network. The hardening iseffected preferably via the intermediate of a preceramic material. Theluminophore precursors can be converted by ammonolysis, polycondensationand pyrolysis to amorphous networks composed of the correspondingelements which are joined to one another by nitrogen. Nitrogen can bereplaced partially by oxygen, which affords oxidic doping.

Activators are incorporated into the luminophore layer, and arepreferably introduced via the following routes.

Those metals which dissolve in liquid ammonia, like europium or barium,are initially charged dissolved in liquid ammonia, and the molecularprecursor, e.g. TADB, is added dropwise. Conversely, the solution of themetals in ammonia can also be added dropwise to initially chargedprecursors, e.g. TADB. The polymeric imide amide formed contains, aswell as the base material elements, for example as well as silicon andboron, also the activator element(s) in homogeneous distribution. Theceramic illuminant is obtained therefrom by pyrolysis.

Activators which do not dissolve in liquid ammonia in elemental form canbe introduced in the form of complex molecular compounds. The ligandsused should preferably contain only elements intrinsic to the system,such as halide (chloride), hydrogen, silicon or boron.

All other elements would be removable from the end product only withadditional complexity, if at all. Particularly suitable metal complexeswhich are compatible with the system are, for example, those with[Cl₃Si(N)SiCl₃]⁻ and chloride as ligands. Since all metals which arepossible activators form binary chlorides from which the desiredcomplexes can be prepared by reaction with Li[Cl₃Si(N)SiCl₃], this routeis universal. The complexes of the activators are dissolved in themolecular precursor, for example in TADB, or optionally dissolvedtogether with the molecular precursor, for example with TADB, in asuitable solvent. This mixture or solution is added dropwise to liquidammonia for the purpose of ammonolysis, or vice versa.

The thickness of the polymer/oligomer layer can be adjusted via theviscosity of the solution and the parameters of the coating process. Theviscosity in turn can be adjusted in a controlled manner via the degreeof polycondensation, i.e. through the mean molar mass of the oligomer,through addition of solvents, through addition of fillers and/or throughthe temperature. The fillers used are preferably materials whichsimultaneously have light-scattering action. Useful examples includeSiO2, TiO2, ZrO2, SnO2 or Ta2O5 with a narrow particle size distributionaround values which, depending on the calculation index of the materialused, optimally scatter white light. The layer thicknesses are adjustedsuch that the pyrolysis gives rise to a crack-free ceramic layer. Thelayer thicknesses are preferably between 200 and 3000 nm, morepreferably between 300 and 2000 nm. The layer thickness achievable in acoating operation depends essentially on the viscosity of the mixture tobe applied and on the application process. If required for an optimaloptical performance of the LED-based light source, the entire coatingprocess may be repeated more than once in order to obtain the desiredlayer thickness.

The final curing to give the luminophore or to give the luminophorelayer is effected preferably by pyrolysis to form an amorphous or partlycrystalline network. In the pyrolysis, the preceramic imide amideobtained as an intermediate in the ammonolysis is converted to the endproduct at temperatures between 600° C. and 1500° C., preferably between1000° C. and 1300° C. The pyrolysis takes place preferably in anatmosphere comprising nitrogen, argon, ammonia or mixtures thereof.

In a preferred embodiment, the layer applied is hardened in an ammoniaatmosphere at room temperature to 200° C. Thereafter, the temperature isincreased stepwise, for example to 620° C., and held at thistemperature. This is followed by pyrolysis, for example at 1050° C. Theheating elements used may be electrical resistance heating ovens orpreferably infrared heaters, mirror ovens or lasers. The entire coatingprocess can be carried out in parallel and continuously (in a conveyorbelt-like manner). For example, the LEDs to be coated can be processedin parallel in a 100×80 matrix arrangement. Different durations of theindividual process steps are balanced out at the same speed of travel bylonger or parallel distances travelled.

1. A light source comprising (i) a primary radiation source and (ii) aluminophore layer based on an amorphous or partly crystalline network,said network comprising N and at least two elements selected from thegroup consisting of P, Si and Al, and at least one activator beingincorporated into the network.
 2. The light source of claim 1, whereinthe activator is selected from the group consisting of Ba, Zn, Mn, Eu,Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, Yb, Sn, Sb, Pb and Bi.
 3. The lightsource of claim 2, wherein the luminophore layer is based on a networkof composition Si₃B₃N₇.
 4. The light source of claim 3, wherein theprimary radiation source emits light in the wavelength range from 250 to450 nm.
 5. The light source of claim 3, wherein the primary radiationsource is an LED.
 6. The light source of claim 4, wherein the primaryradiation source is a GaN⁻ or a Ga(In)N LED.
 7. The light source ofclaim 3, wherein the luminophore layer is in direct or indirect contactwith the primary radiation source.
 8. The light source of claim 3,wherein the luminophore layer comprises a luminophore which emits lightat a wavelength between 480 and 740 nm.
 9. The light source of claim 3,wherein the luminophore layer further comprises solid particles.
 10. Thelight source of claim 9, wherein the solid particles are selected fromthe group consisting of SiO₂, TiO₂, SnO₂, ZrO₂, HfO₂ and Ta₂O₅.
 11. Thelight source of claim 3, wherein the luminophore layer has a layerthickness between 200 and 3000 nm.
 12. A process for producing a lightsource of claim 1, comprising, applying a luminophore precursor directlyor indirectly in liquid form or as a suspension to a primary radiationsource and then hardening the luminophore precursor.
 13. The process ofclaim 12, wherein the luminophore is applied as a preceramic material,especially as a preceramic oligomer.
 14. The process of claim 13,wherein the luminophore is formed from a molecular precursor.
 15. Theprocess of claim 14, wherein the molecular precursor is a one-componentprecursor, especially selected from the group consisting ofCl₃Si(NH)BCl₂(TABD), Cl₃PNSiCl₃, Cl₄P(N)(BCl₂)SiCl₃, (Cl₃Si)₂NBCl₂,Cl₃SiN(BCl₂)₂, (H₃Si)₂NBCl₂, Cl₃Si(NH)(BCl)(NH)SiCl₃,[(Cl₃Si)(NH)(BNH)]₃, Cl₃Si(NH)(AlCl)(NH)SiCl₃, (Cl₃Si(NH)AlCl₂)₂ and[Cl₃PN(PCl₂)₂N]⁺[AlCl₄]⁻.
 16. The process of claim 12, wherein theluminophore precursor is applied by dip-coating, by spin-coating or byspray-coating.
 17. The process of claim 12, wherein the viscosity of theluminophore precursor is adjusted to from 0.01 to 10 Pa·s.
 18. Theprocess of claim 12, wherein the luminophore is applied in a pluralityof layers.
 19. The process of claim 18, wherein the luminophoreprecursor is hardened by pyrolysis.
 20. A wavelength-converting materialcomprising a luminophore layer as defined in claim 1.